Vandervelde Earns Air Force Grant for Photodetection Research
Promising research in infrared photodetection has earned a Tufts
University School of Engineering professor an early-career award
from the Air Force Office of Scientific Research. The Air Force's
Young Investigator Research Program (YIP) annually awards funding to
U.S. scientists and engineers who show exceptional ability and
promise for conducting basic research.
Assistant Professor Tom Vandervelde, the John A. and Dorothy M.
Adams Faculty Development Professor in the Department of Electrical
and Computer Engineering, received a YIP for his work on exploring
and increasing the capabilities of photodetectors with applications
for advances in biomedical diagnostics, health care, and sustainable
Vandervelde will use the $450,000, three-year award to investigate
the properties of nanostructure materials used to enhance the
function of infrared photodetectors—devices that detect or measure
electromagnetic wavelengths that are longer than wavelengths in the
visible light spectrum.
Presently, infrared photodetectors are generally selectively tuned
one particular wavelength. For example, a thermal imaging infrared
camera photodetecting device measures the heat emitted by objects.
With a grant from the Air Force Young Investigators Program,
Assistant Professor Tom Vandervelde is researching the design of
new infrared photodetectors that could detect multiple
wavelengths at the same time. Being able to interpret different
wavelengths of light in the same photodetector could be useful
when distinguishing between objects, such
as being able to detect a person (above) obscured by foliage
Photo credit: FLIR Systems Inc.
Heat is understood by the photodetector as a form of infrared
electromagnetic radiation that can be seen by our eyes when
translated in grayscale. Hotter objects emit more electromagnetic
radiation and appear white; cooler objects appear dark.
"Traditionally, in the infrared, everything is effectively in black
and white," says Vandervelde who says that infrared images are
colored to make the distinctions more pronounced. "The color shows
different emissivity—the ability of objects to emit electromagnetic
radiation—it's not like how we think of color with different
wavelengths; it's all one wavelength, and we're measuring the
relative power intensity that's coming out."
To make photodetectors more useful, engineers like Vandervelde are
working in an area known as “multimodal sensing”—the idea that one
photodetecting device could detect multiple infrared wavelengths at
the same time.
Presently, photodetectors require physically switching a filter to
be able to understand different properties of an object, such as
temperature or material composition. By using metmaterials,
artificial electromagnetic composites, typically made of highly
conducting metals, a filter could be created that could detect
multiple wavelengths by a change in voltage.
"If I look at a white powder with a photodetector that senses
temperature, I can say that this white powder is generally a certain
temperature, but if use a photodetector with multiple wavelengths, I
could actually identify what the material is, as well as its
temperature," says Vandervelde, adding that in the infrared spectrum
a white powder like anthrax could be distinguished from something
like powdered sugar.
Being able to interpret different polarizations of light in the same
photodetector is also useful when distinguishing between natural and
man-made objects, Vandervelde says.
"Natural materials are not smooth, they're very rough. Manmade
materials tend to be very smooth and hard, and they scatter light
differently. If you can take an image and look at it from one
polarization and look at it from another, manmade objects will stand
out, whereas trees and natural materials won't," which could be used
for search and rescue operations, looking for someone through a
dense forest canopy from an airplane, for example, says Vandervelde.
In the biomedical field, a multimodal infrared photodetector could
be used to detect patient hemoglobin and glucose levels at the same
time, with the same device.
Though multimodal sensing devices with what are called "hyperspectral
imaging" arrays do exist, says Vandervelde, they present challenges
being highly complex and computationally intensive, wasting time and
"If a photodetector camera has a 1000 by 1000 pixel array and each
pixel interprets a thousand different wavelengths a second, that's a
billion points of data," says Vandervelde. "It might take a week to
figure out what you saw."
Without an active filtering mechanism designed to selectively
interpret wavelengths, these devices detect all possible wavelengths
and then an end user must sift through the data to find the relevant
"By increasing the functionality of the infrared photodetector, we
can enhance the selectivity of the data actually recorded on the
front end to reduce processing needs on the back end, thereby making
real-time detailed information available,” whether at the patient
bedside, in the military arena, or contaminated environmental sites,
The techniques used to create this tunable photodetector filter
could also have energy applications in creating an anti-reflective
coating for thermophotovoltaic devices and more traditional solar
The AFOSR announced this year it will award more than $16.5 million
in YIP grants to 43 scientists and engineers. According to AFOSR,
the selection committee received 242 proposals in response to the
office's broad agency announcement in major areas of interest to the
Air Force. These areas of interest include: aerospace, chemical and
material sciences; physics and electronics; and mathematics,
information and life sciences.
The objective of this program is to foster creative basic research
in science and engineering, enhance early career development of
outstanding young investigators and increase opportunities for the
young investigators to recognize the Air Force mission and the
related challenges in science and engineering.
[story posted on November 10, 2010]